render/color: return tranform in wlr_color_transform_ref()

This is more consistent with the rest of the wlroots APIs and is
more concise.

include/wlr/render/color.h

@@ -44,7 +44,7 @@ struct wlr_color_transform *wlr_color_transform_init_srgb(void);
 /**
  * Increase the reference count of the color transform by 1.
  */
-void wlr_color_transform_ref(struct wlr_color_transform *tr);
+struct wlr_color_transform *wlr_color_transform_ref(struct wlr_color_transform *tr);
 
 /**
  * Reduce the reference count of the color transform by 1; freeing it and

render/color.c

@@ -20,8 +20,9 @@ static void color_transform_destroy(struct wlr_color_transform *tr) {
 	free(tr);
 }
 
-void wlr_color_transform_ref(struct wlr_color_transform *tr) {
+struct wlr_color_transform *wlr_color_transform_ref(struct wlr_color_transform *tr) {
 	tr->ref_count += 1;
+	return tr;
 }
 
 void wlr_color_transform_unref(struct wlr_color_transform *tr) {

render/vulkan/pass.c

@@ -954,8 +954,7 @@ struct wlr_vk_render_pass *vulkan_begin_render_pass(struct wlr_vk_renderer *rend
 	pass->renderer = renderer;
 	pass->srgb_pathway = using_srgb_pathway;
 	if (options != NULL && options->color_transform != NULL) {
-		wlr_color_transform_ref(options->color_transform);
-		pass->color_transform = options->color_transform;
+		pass->color_transform = wlr_color_transform_ref(options->color_transform);
 	}
 
 	rect_union_init(&pass->updated_region);